The present invention generally relates to planarizing semiconductor wafers, field emission displays, and other microelectronic substrate assemblies used in the fabrication of microelectronic devices. More particularly, the invention is directed towards web-format polishing pads, and methods for making and using web-format polishing pads in mechanical and/or chemical-mechanical planarization of microelectronic substrates.
Mechanical and chemical-mechanical planarizing processes (collectively xe2x80x9cCMPxe2x80x9d) are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic substrate assemblies. FIG. 1 schematically illustrates a planarizing machine 10 with a circular platen or table 20, a carrier assembly 30, a circular polishing pad 40, and a planarizing fluid 44 on the polishing pad 40. The planarizing machine 10 may also have an under-pad 25 attached to an upper surface 22 of the platen 20 for supporting the polishing pad 40. In many planarizing machines, a drive assembly 26 rotates (arrow A) and/or reciprocates (arrow B) the platen 20 to move the polishing pad 40 during planarization.
The carrier assembly 30 controls and protects a substrate 12 during planarization. The carrier assembly 30 typically has a substrate holder 32 with a pad 34 that holds the substrate 12 via suction. A drive assembly 36 of the carrier assembly 30 typically rotates and/or translates the substrate holder 32 (arrows C and D, respectively). The substrate holder 32, however, may be a weighted, free-floating disk (not shown) that slides over the polishing pad 40.
The combination of the polishing pad 40 and the planarizing fluid 44 generally define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The polishing pad 40 may be a conventional polishing pad composed of a polymeric material (e.g., polyurethane) without abrasive particles, or it may be an abrasive polishing pad with abrasive particles fixedly bonded to a suspension material. In a typical application, the planarizing fluid 44 may be a CMP slurry with abrasive particles and chemicals for use with a conventional nonabrasive polishing pad. In other applications, the planarizing fluid 44 may be a chemical solution without abrasive particles for use with an abrasive polishing pad.
To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against a planarizing surface 42 of the polishing pad 40 in the presence of the planarizing fluid 44. The platen 20 and/or the substrate holder 32 then move relative to one another to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate 12.
CMP processes must consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns. Prior to being planarized, many substrates have large xe2x80x9cstep heightsxe2x80x9d that create a highly topographic surface across the substrate. Yet, as the density of integrated circuits increases, it is necessary to have a planar substrate surface at several stages of processing the substrate because non-uniform substrate surfaces significantly increase the difficulty of forming sub-micron features or photo-patterns to within a tolerance of approximately 0.1 xcexcm. Thus, CMP processes must typically transform a highly topographical substrate surface into a highly uniform, planar substrate surface (e.g., a xe2x80x9cblanket surfacexe2x80x9d).
One particularly promising planarizing machine to enhance the planarity of the substrates is a web-format machine that uses a long, flexible polishing pad. FIG. 2 is a schematic isometric view of a web-format planarizing machine 100 similar to a machine manufactured by EDC Corporation. The planarizing machine 100 may have a support table 110 with a base 112 at a workstation A defining a planarizing zone. The base 112 is generally a rigid panel or plate attached to the table 110 to provide a flat, solid surface to which a portion of a web-format planarizing pad 140 is supported during planarization. The planarizing machine 100 also has a plurality of rollers to guide, position, and hold the web-format pad 140 over the base 112. The rollers generally include a supply roller 120, first and second idler rollers 121a and 121b, first and second guide rollers 122a and 122b, and a take-up roller 123. The supply roller 120 carries an unused or pre-operative portion of the web 140, and the take-up roller 123 carries a used or post-operative portion of the web 140. A motor (not shown) drives at least one of the supply and take-up rollers to sequentially advance the web 140 across the base 112. As such, unused portions of the web 140 may be quickly substituted for worn sections. The first idler roller 121a and the first guide roller 122a stretch the web 140 over the base 112 to hold the web 140 stationary during operation.
The planarizing machine 100 also has a carrier assembly 130 to translate the substrate 12 across the web 140. In one embodiment, the carrier assembly 130 has a substrate holder 132 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing process. The carrier assembly 130 may also have a support gantry 134 carrying a drive assembly 135. The drive assembly 135 generally translates along the gantry 134, and the drive assembly 135 has an actuator 136, a drive shaft 137 coupled to the actuator 136, and an arm 138 projecting from the drive shaft 137. The arm 138 carries the substrate holder 132 via another shaft 139. The drive assembly 135 may also have another actuator (not shown) to rotate the shaft 139 and the substrate holder about an axis C-C as the actuator 136 orbits the substrate holder 132 about the axis B-B.
One processing concern associated with web-format planarizing machines is that the web-format polishing pad 140 may produce surface asperities on the substrates, such as gouges, scratches or localized rough areas that exceed normal surface non-uniformities across an adequately planarized substrate. More particularly, conventional web-format polishing pads have a plurality of sections 146 attached to one another along seams 147. As a substrate passes over the pad 140, the seams 147 may gouge the substrate and produce asperities on the substrate surface. The seams 147 may even severely damage a substrate in more aggressive CMP processes or on softer materials. Additionally, the planarizing characteristics may vary from one pad section 146 to another. Therefore, conventional web-format polishing pads have several drawbacks that may adversely impact the planarity of the finished substrates.
In addition to such processing concerns, web-format polishing pads also have several manufacturing concerns. FIG. 3 is a schematic isometric view of a process for making a conventional web-format polishing pad in which a cylindrical body 150 of pad material (e.g., polyurethane) is formed in a mold (not shown). A number of individual circular polishing pads 40, which are generally used with the rotational planarizing machine 10 shown in FIG. 1, are formed from the cylindrical body 150. Each circular polishing pad 40 is generally formed by cutting the cylindrical body 150 along a cutting line substantially normal to the longitudinal center line xe2x80x9cC/Lxe2x80x9d of the cylindrical body 150. To adapt the circular pads 40 for use in a web-format planarizing machine, a rectilinear pad section 146 is then cut from a circular polishing pad 40. The rectilinear pad sections 146 are then attached to one another to form the web-format polishing pad 140 with a plurality of seams 147 (FIG. 2).
One particular manufacturing concern of fabricating web-format polishing pads is that trimming the circular polishing pads 40 to form the rectilinear pad sections 146 is time consuming and wastes a significant amount of pad material. Another manufacturing concern of fabricating web-format polishing pads is that most planarizing machines currently in use require circular polishing pads 40 that fit on a rotating platen. Many pad manufacturers, therefore, are reticent to develop rectilinear molds for forming a rectilinear body of pad material. Thus, it is wasteful and time consuming to use existing polishing pad manufacturing equipment and processes to produce web-format pads.
The present invention is directed towards web-format polishing pads for mechanical and/or chemical-mechanical planarization of microelectronic substrate assemblies, along with methods for making and using such web-format pads. In one aspect of the invention, a web-format polishing pad is made by slicing a cylindrical body of pad material along a cutting line that is at least substantially parallel to a longitudinal centerline of the body and at a radial depth inward from an exterior surface of the body. For example, a web of pad material can be sliced from the cylindrical body by rotating the body about the longitudinal centerline and pressing a cutting element against the rotating cylindrical body along the cutting line. The cutting element can be a knife with a sharp edge positioned at the cutting line and a face extending along a tangent of the cylindrical body. Additionally, an actuator can move the cutting element radially inwardly as the body rotates to continuously peel a seamless web of pad material having a desired thickness from the cylindrical pad body. The web of pad material accordingly may be used on a web-format planarizing machine for planarizing microelectronic substrates.